JP3666388B2 - Martensitic stainless steel seamless pipe - Google Patents

Description

【表２】

これらの焼入れ、焼戻し処理した鋼板から、溶接部の特性を評価するため下記の方法で溶接継ぎ手を製作した。
【００４６】
すなわち、熱処理後の各鋼板から、それぞれ幅７０ｍｍ、長さ４００ｍｍの２枚の溶接継ぎ手用の鋼板を切り出し、圧延方向の側面に開先加工を施して突き合わせて、２５Ｃｒ系のスーパー２相ステンレス鋼の溶接材料を用いてガス・タングステン・アーク溶接（ＧＴＡＷ）法にて溶接した。
【００４７】
焼入れ、焼戻し処理を施したままの鋼板（以下母材という）および溶接継ぎ手から、下記の試験片を加工し、機械的特性と耐食性を調査した。
【００４８】
母材および溶接継ぎ手から製作した試験片
シャルピー衝撃試験片：ＪＩＳ４号シャルピー試験片
試験片の長さ方向が圧延直角方向となるように製作し、溶接継ぎ手からは、溶接熱影響部から切り出し、ノッチ位置はボンドから１ｍｍとした。
母材から製作した試験片
引張り試験片：直径４ｍｍ、標点間距離２０ｍｍ
引張り方向が圧延方向となるように製作
耐食性試験片：、厚さ２ｍｍ、幅１０ｍｍ、長さ７５ｍｍ
耐食性試験は、分圧３０気圧の炭酸ガスを飽和させた８０℃の２５％ＮａＣｌ溶液に、２００時間浸漬して腐食速度を測定した。
これらの試験結果を、表３および表４に示す。
【００４９】
【表３】

【表４】

なお、表３、４中の耐食性の評価は、腐食速度が０．１ｍｍ／年未満の場合を”○”、０．１ｍｍ／年以上の場合を”×”と表示した。
【００５０】
試験Ｎｏ．１〜３４は本発明例で、本発明で規定した化学組成を有する鋼Ｎｏ．Ｓ１〜Ｓ３４を用い、フレッシュマルテンサイト率が７〜８０％の範囲にある。これらの鋼は、引張り強さ８０ｋｓｉグレード（降伏強度：５５０ＭＰａ以上）の高強度を有しながら、８４％以下と降伏比が低く、母材の靭性および耐食性、および溶接部の靭性ともに良好である。
【００５１】
試験Ｎｏ．３５〜３７（鋼Ｎｏ．Ｓ３５〜Ｓ３７：ＡＰＩ１３Ｃｒ相当鋼）は従来例で、フレッシュマルテンサイトを析出させたが、フレッシュマルテンサイトの強度が著しく高いので、いずれも強度が高過ぎ、靭性が低下しているとともに、耐食性が劣っており、また降伏比も高い。
【００５２】
一方、比較例の試験Ｎｏ．３８〜４２は、鋼の化学組成は本発明で規定する範囲内にあり、フレッシュマルテンサイト率が規定範囲から外れている例である。
比較例の試験の試験Ｎｏ．４３〜４６は、マルテンサイト率は本発明の規定を満たしてはいるが、化学組成が本発明で規定する範囲からはずれた例で、いずれも母材および、溶接部の靭性が大幅に低下している。
【００５３】
なお、本実施例は圧延した鋼板で試験をおこなったが、継目無鋼管や溶接鋼管においても同様の特性が得られる。
【００５４】
【発明の効果】
本発明によれば、Ｃｕを添加せずにＮｉを低減しても靭性、耐食性が確保でき、溶接構造物としての安全性が高まる低降伏比を有し、安価で溶接性に優れたマルテンサイト系ステンレス継目無鋼管が提供できる。また、本発明の継目無鋼管は圧延後の冷却の後、１回の熱処理により得られ、製造コストも抑制できる利点を有する。[0001]
BACKGROUND OF THE INVENTION
The present invention is related to a martensitic stainless seamless steel pipe of a low yield ratio superior in toughness and carbon dioxide corrosion. This seamless steel pipe is suitable for applications such as oil well pipes for mining crude oil containing carbon dioxide gas, flow lines for transporting crude oil, line pipes, oil well well bottom equipment and valves.
[0002]
[Prior art]
With the decrease in oil and natural gas resources, development of offshore oil fields as well as onshore has become active. When developing an offshore oil field, an offshore platform will be built as a drilling and refining base, and oil and natural gas will be pumped from the platform through an oil well.
Furthermore, in order to reduce the corrosivity, a method of carrying out purification such as dehydration and desulfurization on a platform and then transporting it through an inexpensive carbon steel or alloy steel pipeline is generally used. However, because the platform construction and maintenance costs are enormous, new offshore oil field mining technologies that do not require platform construction have been developed in recent years.
[0003]
That is, without dropping the oil well pipe from the platform directly to the underground oil reservoir, the oil well pipe is lowered from the sea floor to the underground oil reservoir, and the oil well is finished at the sea floor (sub sea completion), and the highly corrosive crude oil and gas flow as they are. It is a method of transporting to an existing platform on the line. In this case, the flow line needs to have excellent corrosion resistance with respect to the medium to be transported, and a material such as stainless steel or high alloy having corrosion resistance equivalent to that of the oil well pipe is required.
[0004]
It is known that high Cr steel is effective against corrosion caused by carbon dioxide contained in oil wells. For oil well pipes containing a lot of carbon dioxide, 0.2% C-13% specified by API-13Cr. A lot of Cr steel is used. However, since this material has a high C concentration, weldability is not preferable, and it is unsuitable for uses such as flow lines and line pipes that are welded. Therefore, in recent years, a new steel type excellent in weldability, called super 13Cr steel, in which the C content is reduced and Ni is added as an austenite generating element instead has been developed.
[0005]
However, the super 13Cr steel contains a large amount of Ni at 5 to 7% and has a problem that it is significantly more expensive than API-13Cr. Moreover, simply reducing the Ni content not only produces δ ferrite that reduces hot workability, corrosion resistance, and toughness, but also the Ni content itself dominates toughness, making it difficult to ensure toughness.
[0006]
JP-A-9-228001, JP-A-10-1752, and JP-A-11-61267 disclose methods for ensuring toughness in a low C martensitic stainless steel containing 2% or less of Ni. Has been. In any case, the addition of Cu suppresses toughness reduction due to Ni reduction.
[0007]
Japanese Patent Application Laid-Open No. 8-295939 discloses a method for producing a high Cr martensitic steel pipe for a line pipe that improves toughness by heat-treating a low C martensitic stainless steel containing Cu as an essential element.
[0008]
Japanese Patent Laid-Open No. 10-1752 discloses quenching of low C martensitic stainless steel with improved toughness by adding Cu and N, and Japanese Patent Laid-Open No. 11-61267, steel containing Cu as an essential element. A method for producing a martensitic seamless steel pipe is disclosed in which the toughness is improved by performing a heat treatment in a two-phase region between the tempering heat treatment and the tempering heat treatment.
[0009]
As described above, all of the above prior arts ensure toughness by adding Cu to the steel whose toughness is reduced by reducing Ni, or further specify the heat treatment etc. using the steel to which Cu is added. This is an improved technology.
[0010]
However, in stainless steel, Cu may reduce hot workability and creep strength, and is often undesirable as an impurity, and steel added with Cu has a problem in scrap recyclability. Therefore, a method for ensuring toughness without adding Cu has been required.
In addition, in the method of securing toughness by the heat treatment, the number of heat treatments is preferably as small as possible from the viewpoint of production cost, and production by a direct quenching method of quenching without cooling to room temperature after hot working is desirable, In this case, there is a problem that crystal grains become coarse and it becomes more difficult to secure toughness.
[0011]
JP-A-11-61267 discloses a heat treatment method for ensuring the toughness of a direct quenching material. However, after direct quenching, two heat treatments by two-phase region heat treatment and tempering are required, and direct quenching is performed. There was a problem that the effect of reducing the heat treatment due to was not obtained at all.
[0012]
[Problems to be solved by the invention]
The object of the present invention is to provide a low C martensitic stainless steel pipe with a low Ni content of 3% or less and an excellent low toughness and corrosion resistance without adding Cu and without multiple heat treatments. It is to provide a martensitic stainless steel pipe with a yield ratio.
[0013]
[Means for Solving the Problems]
Without the addition of Cu, also without performing multiple heat treatment, toughness even direct quenching material, a result of intensive investigations to develop an inexpensive low C martensitic stainless seamless steel pipe having excellent corrosion resistance, the following We were able to obtain the knowledge of.
[0014]
a) In order to ensure toughness, corrosion resistance and hot workability, δ ferrite must not be generated. In order to suppress the formation of δ ferrite and reduce Ni, it is necessary to add an austenite generating element instead of Ni or to reduce the ferrite forming element.
[0015]
b) Cu, which is an austenite-forming element, has a problem in scrap recyclability, and other austenite-generating elements, C and N, cannot be used because they increase the strength of the weld and reduce toughness and corrosion resistance.
[0016]
c) Therefore, it is necessary to reduce the content of Cr, which is a ferrite-forming element. The API-13Cr in the oil well pipe has a Cr content of about 13%. However, a significant amount of Cr becomes Cr carbonitride and does not contribute to corrosion resistance depending on the C and N content, so it is a low C and low N material. In this case, it is not necessary to secure a Cr content of 13%. If the Cr content is at least 9.5%, carbon dioxide corrosion resistance equivalent to that of API-13Cr can be obtained. Since it produces | generates and hot workability, corrosion resistance, and toughness fall, it is good to make Cr content into 9.5%-12% reduced from API-13Cr.
[0017]
d) When Ni is reduced in a component system not containing Cu, the toughness is reduced, but as a countermeasure, the control of the metal structure is effective, and the toughness can be improved if a mixed structure of tempered martensite and fresh martensite is used. In particular, in order to ensure the toughness of fresh martensite, it is necessary to add a small amount of Mo.
[0018]
e) When the fresh martensite ratio is 1 to 80%, a yield ratio of 85% or less which is good as a welded structure can be obtained.
[0019]
The present invention has been made based on such findings, and the gist thereof is as follows.
[0020]
(1) By mass%, C: 0.03% or less, Si: 0.05-1%, Mn: 0.05-2%, P: 0.025% or less, S: 0.01% or less, Cr : 9.5-12%, Ni: 1-3%, Mo: 0.05-1.5%, N: 0.05% or less, O: 0.01% or less, the balance being Fe and impurities A martensitic stainless steel pipe having a mixed structure of tempered martensite and fresh martensite, the amount of fresh martensite being 1% to 80%.
[0021]
(2) Further, V: 0.001 to 0.5%, Nb: 0.001 to 0.5%, Ti: 0.001 to 0.5%, and Zr: 0.001 to 0.5% The martensitic stainless steel seamless pipe according to (1) above, which contains one or more selected from:
(3) Further, one or more selected from Ca: 0.0005 to 0.05%, Mg: 0.0005 to 0.05%, and REM: 0.0005 to 0.05%. The martensitic stainless steel seamless steel pipe described in (1) above.
[0022]
(4) Further, V: 0.001 to 0.5%, Nb: 0.001 to 0.5%, Ti: 0.001 to 0.5%, and Zr: 0.001 to 0.5% 1 or 2 or more types selected from: Ca: 0.0005 to 0.05%, Mg: 0.0005 to 0.05%, REM: 0.0005 to 0.05% The martensitic stainless steel seamless steel pipe according to the above (1), containing one or more kinds.
[0023]
(5) The martensitic stainless steel seamless pipe according to any one of (1) to (4) , further containing 0.001 to 0.1% of sol.Al.
[0024]
(6) The martensitic stainless steel seamless pipe according to any one of (1) to (5) , further containing B in an amount of 0.0003 to 0.01%.
[0025]
In addition, since it is difficult to discriminate fresh martensite and tempered martensite with an optical microscope, the fresh martensite ratio is obtained by the following formula.
Fresh martensite ratio = (c−b) / (a−b) × 100 (%)
here,
a is the Rockwell C hardness b when water-quenched from 1000 ° C. is the hardness c after quenching and tempering at an Ac1 point temperature of −20 ° C. is the Rockwell hardness C after the final heat treatment.
And However, when the above formula becomes negative, the fresh martensite ratio is set to 0%. Moreover, when precipitation strengthening acts, the calculated value may exceed 100%. In this case, the fresh martensite ratio is set to 100%.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
The reason why the chemical composition and the metal structure are defined in the present invention will be described below. In addition, all the% display of a chemical composition shows the mass%.
[0027]
C:
If the content of C exceeds 0.03%, the strength of fresh martensite increases and the toughness decreases, so the upper limit was set to 0.03%. The lower the C content, the better. The lower the C content, the better the toughness when a mixed structure of tempered martensite and fresh martensite is obtained, so the content is preferably 0.2% or less, more preferably 0.009% or less.
[0028]
Si:
Si is an element necessary for deoxidation, but since it is a ferrite-generating element, if it is added too much, δ-ferrite is generated and hot workability, toughness, and corrosion resistance are reduced. It is necessary to contain 0.05% or more for deoxidation. On the other hand, if it exceeds 1%, ferrite tends to be formed, so the range was made 0.05 to 1%.
[0029]
Mn:
Mn is an element necessary for steelmaking as a deoxidizing material. If it is less than 0.05%, the deoxidizing action is insufficient and the toughness and corrosion resistance are lowered, so the lower limit was made 0.05%. In order not to precipitate δ ferrite at a high temperature, it is preferable to contain a large amount, and an amount exceeding 1% is preferable. On the other hand, if it exceeds 2%, the toughness is lowered, so the upper limit was made 2%.
[0030]
P:
P exists in steel as an impurity, and reduces corrosion resistance and toughness. In order to obtain sufficient corrosion resistance and toughness, it is necessary to be 0.025% or less. However, the lower the content, the better. If severe low temperature toughness is required, 0.02% or less. When severe low temperature toughness is required, 0.015% or less is preferable.
[0031]
S:
S exists in steel as an impurity, and decreases hot workability, corrosion resistance, and toughness. In order to obtain these sufficient characteristics, 0.01% or less is necessary, but the lower the content, the better, and 0.002% or less is preferable.
[0032]
Cr:
Cr is a component that improves carbon dioxide corrosion resistance. If it is less than 9.5%, sufficient carbon dioxide corrosion resistance cannot be obtained, so the lower limit was made 9.5%. In addition, if the upper limit of Ni is 3%, if the upper limit of Ni is 3%, if the Cr content exceeds 12%, δ ferrite is likely to be generated by heating during rolling, and hot workability, toughness, and corrosion resistance. The upper limit was made 12%. As the rolling heating temperature is higher, the deformation resistance is reduced and the tool life is increased, so that a component system in which δ ferrite is not generated even at higher temperature heating is preferable. Therefore, the upper limit of Cr is preferably 11.5%, more preferably 10.9%. Further, in order to secure sufficient corrosion resistance against carbon dioxide gas, the better the result is obtained as the amount of Cr increases, so 10% or more is more desirable.
Ni:
In high Cr steel with a reduced C content, Ni is an essential element for suppressing the formation of δ ferrite and ensuring toughness. If the Ni content is less than 1%, the formation of δ ferrite cannot be suppressed, and the toughness is significantly reduced, so the upper limit was made 1%. From the viewpoint of ensuring toughness, the higher the Ni content, the better. Therefore, the content is preferably 1.5% or more. Although there is no upper limit of Ni from the viewpoint of characteristics, Ni is an expensive element, and if added in a large amount, the cost difference with API-13Cr of the oil well pipe becomes large, so 3% was set as the upper limit. In order to bring the cost closer to the oil well pipe, it is preferable to reduce the Ni addition amount as much as possible, and when pursuing economy, the upper limit is preferably 2.5%, more preferably 2%.
[0033]
Mo:
Mo is an important element in the seamless steel pipe of the present invention, and it is necessary to contain Mo in order to ensure good toughness even in a structure containing fresh martensite that has not been tempered. In order to acquire this effect, it is necessary to make it contain 0.05% or more. Furthermore, since it also has an effect of improving the resistance to sulfide stress cracking, the corrosion resistance improves as the amount increases. However, Mo is an expensive element and the upper limit is set to 1.5% so as not to increase the cost. Therefore, a minimum content is desirable, and a preferable range is 0.05 to 0.5%, and a more preferable range is 0.05 to 0.3%.
[0034]
N:
N is an element that greatly reduces toughness. If the content exceeds 0.05%, the strength of fresh martensite is increased and the toughness is significantly reduced, so the upper limit was set to 0.05%. The lower the N content, the better. The lower the N content, the better the toughness of the tempered martensite and fresh martensite mixed structure. Therefore, the N content is preferably 0.02% or less, more preferably 0.01% or less. It is better to restrict.
[0035]
O (oxygen):
When the content of O exceeds 0.01%, the toughness and corrosion resistance are remarkably lowered.
[0036]
The above chemical composition may further contain the following elements as necessary.
V, Nb, Ti, Zr:
These elements are included for the purpose of obtaining such an effect, which has the effect of improving the strength when it is a mixed structure of tempered martensite and fresh martensite, fixing C, and reducing variation in strength. be able to. If the content of each element is less than 0.001%, those effects cannot be expected, and if it exceeds 0.5%, δ ferrite is generated and the hot workability is reduced, so that it is contained. In each case, the content was 0.001 to 0.5%.
[0037]
sol.Al:
Al is an element that can be added for deoxidation. When added, 0.001% or more is necessary to obtain the above effect. On the other hand, since Al is a strong ferrite-forming element, if the content exceeds 0.1%, δ ferrite is generated, so the upper limit when it is contained is 0.1%.
[0038]
B:
Since B has an effect of improving toughness and hot workability, it is contained when obtaining these effects. In order to acquire the said effect, 0.0003% or more is required, On the other hand, since corrosion resistance will fall when it exceeds 0.01%, when making it contain, it was 0.0003 to 0.01%.
[0039]
Ca, Mg, REM:
Any of these elements is an effective element for improving the hot workability of steel. It also has an action of preventing clogging during casting. To obtain these effects, one or more are selected and contained. However, the above effects cannot be obtained when the content of any element is less than 0.0005%. On the other hand, if the content exceeds 0.05, a coarse oxide is formed, which becomes a pitting corrosion starting point and the corrosion resistance is lowered. Therefore, when it was made to contain, it was 0.0005 to 0.05%, respectively.
[0040]
Fresh martensite rate:
The main metal structures of the stainless steel seamless pipe of the present invention are tempered martensite and fresh martensite, but may further contain extremely small amounts of δ ferrite and precipitates. If the amount of fresh martensite is extremely small, it is difficult to ensure toughness, and it is necessary to be 1% or more in order to ensure toughness. In addition, if too much is present, the strength increases excessively and the toughness decreases, so the fresh martensite ratio is set to 1 to 80%. In order to ensure good toughness, the amount of fresh martensite is desirably the minimum, preferably 1 to 60%, more preferably 1 to 40%.
[0041]
In the present invention, Cu is not added, and in order to greatly improve toughness in a high Cr steel with low Ni, a certain amount of fresh martensite is present in tempered martensite, and a small amount of Mo is further contained. Although the heat treatment is not particularly specified, the metal structure defined in the present invention can be obtained, for example, by performing the following heat treatment after hot working.
[0042]
First, in order to leave fresh martensite, if the final heat treatment is tempering, all of the fresh martensite becomes tempered martensite. Therefore, the final heat treatment needs to be at a temperature higher than the Ac1 point. When heated to a temperature higher than the Ac1 point, austenite is generated, and in the chemical composition defined in the present invention, it does not become retained austenite but undergoes martensitic transformation by cooling. Therefore, a desired structure can be obtained by heating and cooling to a two-phase region of 80% or less austenite and tempered martensite. Also, even if heating to the austenite single phase region, if the subsequent cooling rate is slow, some of the structure is automatically tempered during the cooling after the martensite transformation, so even in this case fresh martensite and tempered martensite And a mixed tissue is obtained. Quantification of fresh martensite is extremely difficult by structural observation, and instead, it is quantified by a calculation formula representing the martensite ratio.
This effect is particularly effective for in-line heat-treated materials with relatively coarse grains that are air-cooled or rapidly cooled immediately after re-rolling at high temperatures where it is difficult to ensure toughness. Direct quenching after hot working Further, the heat treatment is particularly effective in the heat treatment in which heating and cooling are performed in a temperature range of Ac1 point to Ac3 point and no subsequent tempering is performed. Moreover, it is good also as a structure | tissue where the tempered martensite and fresh martensite which were self-tempered by heating to Ac3 point or more and letting it cool are mixed.
[0043]
In the prior art, in-line heat treatment could not secure toughness, and two heat treatments, quenching and tempering after rolling, were necessary. Since good characteristics can be obtained, there is an advantage that in-line heat treatment is possible.
[0044]
【Example】
Stainless steels having the chemical compositions shown in Tables 1 and 2 were melted and then hot forged, and further hot rolled to finish a steel sheet having a thickness of 12 mm, a width of 180 mm, and a length of 700 mm. All finishing temperatures were set to 1000 ° C., and immediately after finishing, they were placed in a furnace at 950 ° C., soaked for 10 minutes, then water-cooled and directly quenched. Next, the fresh martensite ratio was changed by variously changing the temperature of the final heat treatment.
[0045]
[Table 1]

[Table 2]

From these quenched and tempered steel plates, weld joints were produced by the following method in order to evaluate the properties of the welds.
[0046]
That is, from each steel plate after the heat treatment, two steel plates for welding joints each having a width of 70 mm and a length of 400 mm are cut out, faced in the rolling direction and subjected to groove processing, and then 25Cr-based super duplex stainless steel. Welding was performed by gas / tungsten arc welding (GTAW) method.
[0047]
The following specimens were processed from a steel plate (hereinafter referred to as a base material) and a welded joint that had been subjected to quenching and tempering treatment, and the mechanical properties and corrosion resistance were investigated.
[0048]
Specimen Charpy impact test piece manufactured from base metal and welded joint: JIS No. 4 Charpy test piece test piece is manufactured so that the length direction is perpendicular to the rolling direction. The position was 1 mm from the bond.
Test piece tensile test piece made from base material: Diameter 4mm, distance between gauge points 20mm
Corrosion resistance test piece manufactured so that the tensile direction is the rolling direction: Thickness 2 mm, width 10 mm, length 75 mm
In the corrosion resistance test, the corrosion rate was measured by immersing in a 25% NaCl solution at 80 ° C. saturated with carbon dioxide gas having a partial pressure of 30 atm for 200 hours.
These test results are shown in Tables 3 and 4.
[0049]
[Table 3]

[Table 4]

In the evaluation of corrosion resistance in Tables 3 and 4, “○” was indicated when the corrosion rate was less than 0.1 mm / year, and “X” was indicated when the corrosion rate was 0.1 mm / year or more.
[0050]
Test No. 1 to 34 are examples of the present invention, and steel Nos. Having the chemical composition defined in the present invention. Using S1 to S34, the fresh martensite ratio is in the range of 7 to 80%. These steels have a high strength of 80 ksi grade tensile strength (yield strength: 550 MPa or more), but have a low yield ratio of 84% or less, and both the toughness and corrosion resistance of the base metal and the toughness of the weld are good. .
[0051]
Test No. 35 to 37 (steel No. S35 to S37: API13Cr equivalent steel) is a conventional example, and fresh martensite is precipitated. However, since the strength of fresh martensite is remarkably high, both strengths are too high and toughness decreases. In addition, the corrosion resistance is inferior and the yield ratio is high.
[0052]
On the other hand, test No. of the comparative example. Nos. 38 to 42 are examples in which the chemical composition of steel is within the range specified in the present invention, and the fresh martensite ratio is out of the specified range.
Test No. of the comparative example test Nos. 43 to 46 are examples in which the martensite ratio satisfies the provisions of the present invention, but the chemical composition deviates from the range defined in the present invention. In both cases, the toughness of the base material and the welded portion is greatly reduced. ing.
[0053]
In addition, although the present Example tested on the rolled steel plate, the same characteristic is acquired also in a seamless steel pipe or a welded steel pipe.
[0054]
【The invention's effect】
According to the present invention, martensite having low yield ratio that can secure toughness and corrosion resistance even when Ni is reduced without adding Cu, and safety as a welded structure is increased, and is excellent in weldability. Stainless steel seamless steel pipe can be provided. Moreover, the seamless steel pipe of the present invention is obtained by a single heat treatment after cooling after rolling, and has an advantage that the manufacturing cost can be suppressed.

Claims (6)

In mass%, C: 0.03% or less, Si: 0.05-1%, Mn: 0.05-2%, P: 0.025% or less, S: 0.01% or less, Cr: 9. 5-12%, Ni: 1-3%, Mo: 0.05-1.5%, N: 0.05% or less, O: 0.01% or less, with the balance being Fe and impurities, A martensitic stainless steel seamless pipe characterized in that the metal structure is a mixed structure of tempered martensite and fresh martensite, and the amount of fresh martensite is 1 to 80%. In mass%, C: 0.03% or less, Si: 0.05-1%, Mn: 0.05-2%, P: 0.025% or less, S: 0.01% or less, Cr: 9. 5-12%, Ni: 1-3%, Mo: 0.05-1.5%, N: 0.05% or less, O: 0.01% or less, and V: 0.001-0 0.5%, Nb: 0.001 to 0.5%, Ti: 0.001 to 0.5%, and Zr: One or more selected from 0.001 to 0.5% and the balance being Fe and impurities, martensitic stainless seamless steel tube amount of mixed structure and a by fresh martensite metal structure tempered martensite and fresh martensite is characterized by a 1 to 80% . In mass%, C: 0.03% or less, Si: 0.05-1%, Mn: 0.05-2%, P: 0.025% or less, S: 0.01% or less, Cr: 9. 5-12%, Ni: 1-3%, Mo: 0.05-1.5%, N: 0.05% or less, O: 0.01% or less, and Ca: 0.0005-0 .05%, Mg: 0.0005 to 0.05%, REM: 0.0005 to 0.05%, or one or more selected from the group consisting of Fe and impurities, A martensitic stainless steel seamless pipe characterized in that the structure is a mixed structure of tempered martensite and fresh martensite, and the amount of fresh martensite is 1 to 80%. In mass%, C: 0.03% or less, Si: 0.05-1%, Mn: 0.05-2%, P: 0.025% or less, S: 0.01% or less, Cr: 9. 5-12%, Ni: 1-3%, Mo: 0.05-1.5%, N: 0.05% or less, O: 0.01% or less, and V: 0.001-0 0.5%, Nb: 0.001 to 0.5%, Ti: 0.001 to 0.5% and Zr: one or more selected from 0.001 to 0.5%; and Ca: 0.0005-0.05%, Mg: 0.0005-0.05%, REM: One or more selected from 0.0005-0.05%, the balance Is composed of Fe and impurities, the metal structure is a mixed structure of tempered martensite and fresh martensite, and the amount of fresh martensite is 1 to Martensitic stainless seamless steel tube, characterized in that 0%. The martensitic stainless steel seamless pipe according to any one of claims 1 to 4, which contains 0.001 to 0.1% of sol.Al instead of a part of Fe. The martensitic stainless steel seamless pipe according to any one of claims 1 to 5, which contains 0.0003 to 0.01% of B instead of a part of Fe.